Despite immunization of high risk persons against influenza, annual epidemics continue to pose an important threat to the health of persons over the age of 65 years as well as to persons with cardiopulmonary and other high risk conditions. Healthy children are felt to be an important source for community transmission of influenza. Immunizing school-aged children has been proposed as one strategy to protect high risk individuals;by immunizing children spread of influenza is prevented and persons at high risk for complications are protected. The goal of this randomized clinical trial is to determine whether immunizing children in Hutterite colonies with inactivated influenza vaccine can prevent influenza and its complications in other colony members. Furthermore, the study will assess the indirect benefit to Hutterites at high risk of complications. The majority of Hutterites live in Alberta, Saskatchewan, and Manitoba where they practice communal farming on small colonies isolated from towns and cities. We propose a blinded, cluster randomized controlled trial among Hutterite colonies to test the hypothesis that high immunization rates (>70%) of healthy children with inactivated influenza vaccine reduces transmission of influenza to other colony members. Randomization of these homogeneous, moderately sized colonies where there is regular spread facilitated by a communal lifestyle, but limited re-introduction because of relative isolation from outside community, represents a unique opportunity to test the hypothesis of indirect benefit under close to ideal conditions. The primary outcome will be laboratory-confirmed influenza. Secondary outcomes include influenza-like illness, otitis media, physician visits, antimicrobial prescriptions, absenteeism, lower respiratory tract infection, hospitalizations, and death. We believe that the trial we propose will lead to important data that can inform policy on influenza immunization strategy.